1. Field of the Invention
The present invention generally relates to a system and method for mounting instruments and more particularly to a mounting apparatus and method for a fiber optic strain gage carrier.
2. Description of Related Art
Over the past decade fiber optics based sensors have become widely and accepted established in various markets. Fiber optic based sensors are used in numerous applications including the measurement of temperature, displacement, and strain. Some fiber optic sensors are used to extend the measurement of strain and temperature to measure other physical characteristics such as acceleration. Fiber optic sensors may offer several benefits over other types of sensors including reduced sensitivity to electromagnetic interference. Fiber optic sensors are also capable of being multiplexed such that several sensors can operate off of a single optical fiber and can be provided in a small form factor, allowing use in tight spaces.
During use various physical phenomena cause changes in the optical characteristics of a fiber optic based sensors and are used to measure temperature, displacement and strain. Fiber optic strain gages, for instance, do not rely on changes in electrical resistance, inductance or capacitance associated with conventional types of strain gages. Instead, fiber optic strain gages use the correlation of strain or temperature to optical properties such as wavelength frequency, optical phase changes, optical transmittance and optical wave interference.
In some strain gage sensors, one or more fiber Bragg gratings act as the active sensing element. A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. Fiber Bragg gratings are implemented in an optical fiber core as specialized changes to the index of refraction. Strain gages using fiber Bragg gratings may be inherently immune to electromagnetic interference from radio waves, static electricity or lightning discharges. Fiber Bragg grating strain sensors can be connected serially thus dramatically reducing electrical connections and associated cost. The only connection required between serial sensors is an optical fiber. Due to the low signal loss in fiber optics, these strain gages can often be located at a significant distance from any optical strain or temperature gage interrogation and recording instrumentation. Fiber optical strain gages often exhibit better accuracy, repeatability and sensitivity than their conventional counterparts. Fiber optical strain gages can also be located in places that would not otherwise accommodate a large number of individual wires needed for conventional strain gages. In addition, the sensing element of fiber Bragg grating based strain sensors does not typically require active electronics during operation. This helps to ensure safe use of these strain gages in environments where accidental sparks may cause fires or lead to catastrophic explosions, such as certain oil and gas and other industrial environments. Oftentimes, these characteristics make fiber optic based sensors a feasible choice for these hazardous environments.
Despite the favorable characteristics of certain types of sensors, such as fiber Bragg grating based strain sensors, certain limitations may exists. For example, current fiber Bragg grating-based strain sensors often have operating temperature limitations that may limit their potential uses. For example, certain sensors may not be used where the temperature at or near a surface of a test object is outside of the accepted operating temperature range.
Accordingly, there is a desire for a system and method for using fiber optic sensors that enables them to be used in environments that may otherwise be outside of their operational limits, such as a high temperature environment, while maintaining operational characteristics, such as measurement accuracy.